Toward a more maneuverable rear axle

ZF Friedrichshafen has designed a new-generation active kinematics control active rear-axle steering, referred to as AKC, that the German supplier believes represents improvements on several fronts.

The driving system offers customers, even in the heavy-duty market, better maneuverability, autonomous driving applications and benefits in trailering and parking, ZF said.

The technology will appear on the GMC Hummer EV pickup, scheduled to go on sale this fall.

ZF's innovation is a steer-by-wire application that the supplier says supports advanced driver-assistance features and automated driving functions. The second-generation design also enhances the system's vehicle motion control properties, the company said.

ZF's first-gen AKC went into production on the Porsche 911 in May 2013. The second generation is based on a new electronic architecture, with enhancements for both battery-electric vehicles and heavy-duty truck platforms, said Neb Stevanovich, ZF's senior manager of product line chassis actuators.

"We have the ability to deploy the system in anything from a general pickup truck to a heavy-duty pickup truck, all the way to a heavy-duty electric pickup truck," Stevanovich told Automotive News. "ZF has tailored the product to support all of those different integration points.

"We can reduce, for a full-size pickup truck, the turning circle by over 9 feet, which effectively makes a full-size crew cab pickup truck the equivalent of a small SUV or a passenger car," Stevanovich added. "It makes the vehicle that much more comfortable, much more nimble and it's much easier to park."

The enhanced nimbleness will support the advent of automated parking features, he said. That will be important in the era of autonomous driving, when passengers might be in nontraditional seating positions, no longer necessarily forward-facing as a vehicle maneuvers and parks.

"Our AKC system provides a tremendous physiological benefit to all of the different occupants in the vehicle."

Active kinematics control "was birthed out of making improvements to the overall chassis performance," Stevanovich said. But for the second iteration, ZF enhanced the performance, networking and cybersecurity capabilities for electric and autonomous applications.

To eliminate the steering wheel "kick" often felt with electronically controlled power steering systems, ZF introduced a "spindle" design.

"Spindle technology really provides the safest approach for these rear-steering actuators," Stevanovich said. "We've done a number of tests across all different segments and we're very confident in that by-wire technology, so you won't get that steering wheel kick."

ZF engineers gave the system an improved adjustment stroke that now allows the rear wheels to turn by 10 to 12 degrees, he said. The larger steering angle supports electric vehicles, which are often weighed down by heavy batteries and have a longer wheelbase. For heavy-duty applications, the company doubled the system's motor size to get double output capability.

ZF's first AKC has been supplied to more than 500,000 vehicles. ZF's redesign did not require much change in the manufacturing process, Stevanovich said, but did require ZF to expand production capacity in Lebring, Austria, where fourth and fifth assembly lines were recently added.

Before, ZF could produce 250,000 AKC units with a central actuator and 50,000 AKC units with dual actuators annually. For the new generation it will be able to produce more than 1 million units a year.

The company also is considering other manufacturing locations as it takes on U.S. customers.